It is advantageous in many orthopedic applications for bone to grow into, around and/or even completely through, implants designed to support or replace various musculoskeletal structures. Many porous structures exist in the prior art that are designed to receive growing bone or other musculoskeletal tissue. In combination with and in addition to these structures, various bioactive materials are known that passively support or promote the growth of bone and other tissues. Substances that passively support the growth of bone are known as osteoconductive. Osteoconductive substances passively support the ingrowth of bone by being conducive to the growth of vascular structures and osteoprogenitor cells necessary for the growth of bone. Substances that actively stimulate or promote the growth of bone are known as osteogenic or osteoinductive. Specifically, osteogenic substances stimulate the formation of bone, and osteoinductive materials support the mitogenesis of undifferentiated perivascular mesenchymal cells. This osteoinductive activity may lead to the formation of osteoprogenitor cells with the capacity to form new bone.
It is a continuing challenge in the art to produce implants that provide adequate structural support while also providing structures into which bone will actively grow. Some implants include structures that are appropriately shaped to receive growing bone and support musculoskeletal tissues, but lack effective placement of osteoconductive or osteoinductive materials to support the growth of bone throughout or where most advantageous. Other implants include sufficient osteoconductive or osteoinductive materials, but are not formed to provide adequate structural stability and/or to permit bone to grow into portions of the implant that would be advantageous. Therefore, a need exists for implants and for methods of making implants that are both structurally adequate and support or promote bone growth into or through the implants.